<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8" />
    <title>Document</title>
    <script src='lib/webgl-utils.js'></script>
    <script src='lib/webgl-debug.js'></script>
    <script src='lib/cuon-utils.js'></script>
</head>
<body onload="main()">
<canvas id="mybox" width="500" height="500">
    请更换新版浏览器查看效果!
</canvas>
<script >
// 添加平移的uniform分量
let VSHADER_SOURCE=`
attribute vec4 a_position;
uniform vec4 u_translation;
void main(){
    gl_Position=a_position+u_translation;
    }`;
let FSHADER_SOURCE=`
void main(){
gl_FragColor=vec4(1.0,1.0,0.0,1.0);
}`;


    function main(){
        let canvas=document.getElementById('mybox');
        let gl=getWebGLContext(canvas);
        if(!initShaders(gl,VSHADER_SOURCE,FSHADER_SOURCE)){
            console.log('初始化shader失败');
            return;
        }
        let n=initVertexBuffers(gl);
        if(n<0){
            consoel.log('设置顶点位置失败');
            return;
        }
        gl.clearColor(0.0,0.0,0.0,1.0);
        gl.clear(gl.COLOR_BUFFER_BIT);
        gl.drawArrays(gl.TRIANGLE_STRIP,0,n);


    }

    function initVertexBuffers(gl){
        let vertices=new Float32Array([-0.3,0.3,  -0.3,-0.3,  0.3,0.3,  0.3,-0.3]);
        let Tx=0.5,Ty=0.5,Tz=0.0;
        let n=4;
        let vertexBuffer=gl.createBuffer();
        gl.bindBuffer(gl.ARRAY_BUFFER,vertexBuffer);
        gl.bufferData(gl.ARRAY_BUFFER,vertices,gl.STATIC_DRAW);
        let a_position=gl.getAttribLocation(gl.program,'a_position');
        // 获取uniform变量的存储位置
        let u_translation=gl.getUniformLocation(gl.program,'u_translation')
        if(a_position<0){
            console.log('a_position 不存在');
            return ;
        }
        if(u_translation<0){
            console.log('u_translation 不存在');
            return ;
        }
        gl.vertexAttribPointer(a_position,2,gl.FLOAT,false,0,0);
        gl.uniform4f(u_translation,Tx,Ty,Tz,0.0)
        gl.enableVertexAttribArray(a_position);
        return n;

    }

</script>

</body>
</html>